Field of the Invention
The invention relates to a measuring device and a method for determining mass and/or mechanical properties of a biological system.
Description of the Prior Art
Measuring devices for determining mass and/or mechanical properties of biological systems are known from the state of the art.
In Park K, Jang J, Irimia D, Sturgis J, Lee J, Robinson J P, Toner M, Bashir R. Living cantilever arrays for characterization of mass of single live cells in fluids. Lab on a Chip. 8:1034-41 (2008) cantilever arrays are developed to determine mass of cells in solution. These arrays are formed by two sets of cantilevers opposing each other. External sinusoidal power sources are connected to the opposing cantilever sets with a phase shift of 180° in order to generate a nonuniform electric field, which captures cells by dielectrophoresis. There is no active excitation method to oscillate the cantilevers. The cantilevers vibrate only due to thermal noise, which decreases the sensitivity and temporal resolution of this device to measure mass changes. Before starting mass measurements, several days, usually three days, are required for the cells to grow on the cantilevers. That means random cells are selected for the experiments. Due to the design of this device, its use is not compatible with modern optical microscopy techniques for biology, for example differential interference contrast (DIC), fluorescence, confocal or phase contrast microscopy. These techniques are very important in biology since they give additional morphological and functional information about the characterized cell or biological system.
The work of Park K, Millet L J, Kim N, Li H, Jin X, Popescu G, Alum N R, Hsia K J, Bashir R. Measurement of adherent cell mass and growth. PNAS, 107: 20691-6 (2010) shows a device that uses micro-membrane resonators to determine the mass and mechanical properties of single adherent cells in fluid. The membranes are actively excited using the Lorentz's force. To do that the membranes are immersed into a uniform magnetic field and an alternating electrical current flows through the membranes. The movement of the membrane is detected by using a laser Doppler interferometer (LDI). In order to attach cells to the membranes, cells are cultured on the device. Doing so, some cells will randomly adhere to the top of the membranes. Once the cells are injected into the device, at least two hours of waiting time are required before starting the measurements, which importantly limits the cellular processes to be studied. This system is compatible with fluorescence but not with DIC or phase contrast microscopy.
The device in S. Son, A. Tzur, Y. Weng, P. Jorgensen, J. Kim, M. W. Kirschner, S. R. Manalis. Direct observation of mammalian cell growth and size regulation. Nat. Methods. 9:910-2 (2012) is based on a micro-channel resonator, which is a hollow cantilever surrounded by vacuum. Suspended cells floating in a fluid can be pumped into and through the cantilever. When a cell passes by the free end of the cantilever, its buoyant mass increases the total mass of the cantilever, which decreases the resonance frequency of the cantilever. Furthermore, high-resolution fluorescence microscopy can be conducted only for cells passing through a separate reservoir but not when cells pass the mass sensor. This tool is not suitable for adherent cells, since the cells have to be suspended to be able to float through the cantilever. Furthermore, some cellular processes cannot be studied because the device can only detect buoyant masses. Another negative issue of this assay is that both the fluorescence signal (e.g., microscopy) and the buoyant mass of a single cell can be neither acquired continuously over a long period (>>1 second) nor simultaneously, making it very difficult to correlate buoyant mass and cell state.
It is an object of the invention to improve these known devices.